Protective film with release surface

ABSTRACT

Films for use in protecting surfaces are disclosed and comprise at least one release layer and optionally an adhesion layer and/or an intermediate layer, the release layer having a plurality of three-dimensional protrusions that are either formed integral with the release layer or are discrete polymer beads applied to the release layer.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of the PCT/US2009/003844 (filed Jun.26, 2009), which claims the benefit of U.S. Provisional PatentApplication No. 61/133,356, filed Jun. 27, 2008.

BACKGROUND

The disclosure relates to films for use in protecting substrate surfacesduring manufacturing, storage, transport or use. The disclosure alsorelates to a method for making the films.

Surface protection films, also known as masking films, are typicallyused to provide a physical barrier to prevent damage, contamination,scratching, scuffing, or other marring of a substrate. Masking films maybe used to provide such protection during manufacture, shipping, orstoring prior to use of the substrate, for example. Such films may beused in numerous applications as protective coverings for surfaces,particularly for protecting relatively smooth surfaces, such asacrylics, polycarbonates, glass, polished or painted metals and glazedceramics. Optical substrates for televisions, monitors, and otherdisplays, for example, require masking films that both protect thesurface and may be removed without damaging, leaving residues of anadhesive, or other contaminants or particulates on the surface.

Traditionally, masking films have comprised corona-treated films oradhesive-coated paper or film. Corona-treated films are films that havebeen exposed to an electrostatic discharge to oxidize the surface of thefilm. This oxidation increases the film's surface tension and attractionto polar surfaces. Such corona-treated films typically are smooth filmsand rely on very precise corona treatment to facilitate adhesion. Unlessembossed, corona-treated films are typically subject to wrinkling, whichmakes it difficult to use and handle the films. A further disadvantageis that the adhesion promoting effects of corona treatment dissipatewith time.

Generally, conventional masking films are relatively difficult to useand handle. Because masking films are designed to adhere to a surface,they may also adhere to themselves when the masking film is wound on aroll or the adhesion surface otherwise contacts a portion of the maskingfilm. Blocking, as it is called, may result in processing difficultiesincluding delays and wasted material. To reduce the tendency for selfadherence, masking films may be coated with a weak adhesive. The weakadhesive on the masking film may prevent the film from adhering tightlyto itself on the roll, however, the weak adhesive may also not providesufficient adherence to the surface to be protected.

Other films may be provided with one matte surface opposite the adhesionsurface; often called one side matte (“OSM”) masking films. Theirregularity of a matte surface does not provide a good surface foradhesion and provides antiblocking properties to the masking film.

There is a need for a masking film that has a low self adherence butprovides sufficient adherence to a substrate to provide suitableprotection. There is a further need for a masking film that has acushioning effect and eases handling of flat substrates.

In other applications, it may be desired to use materials that do notadhere to the surface, but instead are interleaved with the substratesto provide a physical separation. Such applications are commonly used inmanufacturing operations where, for example, optical grade glass orplastic substrates are tacked together. In such applications, paper orother materials are used to interleave with the substrates to protectagainst damage. The interleaving sheets are also used between stackedfragile and scratch sensitive substrates and to provide separationbetween very smooth optical substrates during shipment to end users.

Accordingly, there is also a need for low cost, non-adhering materialsfor use in protecting substrate surfaces.

SUMMARY

In an embodiment, a masking film comprises a polymeric film web havingat least one three-dimensional release surface.

In one embodiment, the three-dimensional release surface comprises aplurality of raised protrusions formed integral with the film.

In one embodiment, the raised protrusions comprise a plurality ofspaced-apart ribs

In one embodiment, the three-dimensional release surface comprisespolymer nubs.

In one embodiment, the masking film comprises an adhesion layer oppositethe three-dimensional release surface.

These and other embodiments will become apparent upon a further readingof the specification with reference to the drawing and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a masking film shown adhered to asubstrate and comprising a release layer and an adhesion layer, whereinthe release layer comprises a three-dimensional release surface having aplurality of apertured protrusions.

FIG. 1A is a cross sectional view of a masking film shown adhered to asubstrate and comprising a release layer and an adhesion layer whereinthe release layer comprises a three-dimensional release surface having arhomboid embossed pattern.

FIG. 1B is a cross sectional view of a masking film shown adhered to asubstrate and comprising a release layer and an adhesion layer whereinthe release layer comprises a multiplanar film.

FIG. 2 is a cross sectional view of a masking film having a firstrelease layer, a core layer, and a second release layer, wherein eachrelease layer comprises a three-dimensional release surface having aplurality of unapertured protrusions.

FIG. 3 is a cross sectional view of a masking film comprising a singlelayer film having two release surfaces.

FIG. 4 is a perspective view of a masking film having an adhesion layerand a release layer with a three-dimensional release surface comprisingspaced apart longitudinal ribs.

FIG. 4A is a cross sectional view of a masking film similar to theembodiment of FIG. 4, except without any adhesion layer.

FIG. 5 is a perspective view of a masking film having an adhesion layerand a release layer having a three-dimensional surface comprisingpolymer beads.

FIG. 5A is a cross sectional view of the masking film of FIG. 5, as seenalong line and arrows A-A of FIG. 5.

FIG. 6 is a cross sectional view of another embodiment of a film withtwo three-dimensional release surfaces.

FIG. 7 is a schematic illustration of a vacuum lamination process.

FIG. 8 is a schematic illustration of an embossing and/or vacuum formingprocess useful in making certain of the embodiments.

DETAILED DESCRIPTION

Masking films are described in U.S. Pat. Nos. 4,395,760; 5,100,709;5,693,405; 6,040,046; 6,326,081; and 6,387,484 which are herebyincorporated by reference.

As used throughout this disclosure, the singular forms “a,” “an,” and“the” include plural reference unless the context clearly dictatesotherwise. Thus, for example, a reference to “a layer” includes aplurality of layers.

A “laminate” or “composite,” as used herein to describe webs or filmsare synonymous. Both refer to a web structure comprising at least twowebs or films joined to form a multiple-layer unitary web. The webs maybe coextruded or joined by a lamination process, including adhesivelamination, thermal lamination, pressure lamination, and combinationsthereof, as well as other lamination techniques known to those in theart. Adhesives used to form the laminate may be any of a large number ofcommercially available pressure sensitive adhesives, including waterbased adhesives such as, but not limited to, acrylate adhesives, forexample, vinyl acetate/ethylhexyl acrylate copolymer which may becombined with tackifiers. Other adhesives include pressure sensitive hotmelt adhesives or double sided tape.

As used herein, the term “polymer” includes homopolymers, copolymers,such as, for example, block, graft, impact, random and alternatingcopolymers, terpolymers, etc., and blends and modifications thereof.Furthermore, unless otherwise specifically limited, the term “polymer”is meant to include all possible stereochemical configurations of thematerial, such as isotactic, syndiotactic and random configurations.

Handling of substrates having extremely flat surfaces such as panes ofglass, sheets of optical material for monitors, televisions or otherdisplays, or other similar substrates may be difficult. When trying toremove one sheet of such substrates from on top of another sheet, thesheets tend to stick together. The substrate sheets may stick togetherbecause air may not be present or be able to flow between the sheets.The lack of air results in a vacuum between the sheets and, at times,the second sheet will actually be lifted along with the first sheet.However, the second sheet may only lift a short distance before thevacuum is released and the second sheet falls. This drop may result inirreparable damage to the second sheet.

To provide a solution for this handling problem, embodiments of themasking film comprise a release layer having a three-dimensional releasesurface. In some embodiments, the masking film comprises an adhesionlayer and a release layer with a three-dimensional release surface. Inother embodiments, the masking film comprises two three-dimensionalrelease surfaces located on opposite sides of the film. The maskingfilms may comprise a single layer or multiple layers. Intermediatelayers may be interposed between the adhesion layer and the releaselayer or between the two release layers.

Further embodiments include masking films comprising two releasesurfaces. Such masking films may additionally comprise intermediatelayers between the release layers. Each release layer has athree-dimensional release surface. Embodiments comprising two releasesurfaces are advantageous for use in replacing paper elements in stacksof optical substrates.

Substrates with a masking film according to the embodiments placedbetween them are prevented from adhering to each other by creating a gapbetween stacked sheets allowing for an air space between the substratesheets.

Generally, embodiments of the release layer comprise films. As usedherein, a “film” refers to a thin sheet or web comprising a polymer. Afilm may be produced, for example, by extruding a molten thermoplasticpolymer in an extrusion cast or blown process. The polymer may befurther processed between rollers and cooled to form the web. Films canbe monolayer films, coextruded films, and composite films, for example.Composite films may be produced by a coextrusion process or by bondingone or more films together.

A film may be dimensionally described as having a machine direction, across direction, and a z-direction. The machine direction is defined bythe direction in which the film passes through the manufacturingprocess. Typically, films are produced as long sheets or webs which havea much longer length than width, in such a case the machine direction isusually the length (also referred to as the x-direction) of the sheet.

Perpendicular to the machine direction is the cross direction ortraverse direction (also referred to as the y-direction or width) of thesheet. The thickness of the film is measured in the z-direction. Thez-direction of a three-dimensional formed film includes the height ofany three-dimensional features of the formed film and the thickness ofthe film.

A three-dimensional formed film is a film that has been processed toform three-dimensional features on at least one surface of the film.Therefore, three-dimensional formed films have a z-directionmeasurement, loft, that is significantly greater than the nominalthickness of the film. Typically, the loft is at least one and a halftimes the nominal thickness of the film. Examples of three-dimensionalformed films are films that have a plurality of protrusions extendingfrom a continuous land area which protrusions may be apertured orunapertured.

In certain embodiments the three-dimensional formed film may comprise amultiplanar film. Multiplanar films are films that have a continuoussurface and a discontinuous surface spaced from one another in thez-direction. Multiplanar films are distinguished from three-dimensionalfilms in that the protrusions may originate from either the continuoussurface or the discontinuous surface, or both. Protuberances may beformed on any or all of the available planes. Examples of multiplanarfilms are disclosed in U.S. Pat. No. 7,518,032, the disclosure of whichis incorporated herein by reference.

The three-dimensional features of the three-dimensional formed films maybe produced using any suitable process. Most commonly, an embossingprocess, a hydroforming process, or a vacuum forming process, may beused to advantage. The three-dimensional features may have across-section that is circular, oval, triangular, square, pentagonal,hexagonal, or any other desired shape.

The pattern of the protrusions of the three-dimensional film may existin either a regular geometric array or a random array. Typical arrays ofregular geometric patterns can include, but are not limited to,continuous lines (raised ribs) that are straight or wavy, protrusions onstraight or wavy lines, on a 60 degree equilateral triangle array, asquare pattern array, or an array that has mixed spacing and angles butis repeating in clusters or groups of protrusions. Random arrays arerandom without any regular repeating pattern of individual protrusion orof clusters or groups of protrusions.

Formed films can be created, for example, by drawing a polymeric webagainst a forming structure using a vacuum or forcing the web againstthe forming structure using high pressure jets or air or water. Suchprocesses are known from the teachings of US 2004/0119208 and US2004/0119207, and the prior art references cited therein. The disclosureof these published applications, and those of the prior art citedtherein, are incorporated herein by reference. In a direct cast vacuumformation process, a molten polymer is extruded from a die directly ontoa forming structure and then subjected to vacuum to draw the polymerinto apertures in the forming structure. The film is cooled, the shapeof the film is set and the film is removed from the forming structure.The portions of the polymer that were drawn into the apertures in theforming structure result in the protrusions. The level of vacuum andother process parameters can be adjusted to draw the polymer into theapertures and form the protrusions without rupturing the film, or theprocess can be practiced to rupture the film to form apertures at theapex of the protrusion.

In other embodiments, the release layer may be a formed film created bya hydroforming process in which the three-dimensional protrusions areformed by directing high pressure streams of water against the surfaceof a polymer film while the film is supported on a forming structure.The high pressure water will force the film into apertures in a formingscreen in the same manner as the vacuum to create the protrusions. Inother embodiments, the release layer may be a formed film made in areheat process in which a precursor polymeric film is heated to close tothe melting point and then subjected to vacuum while supported on aforming structure as in the direct cast vacuum process described above.As used herein, the term “apertured formed film” refers to athree-dimensional formed film with apertures or holes at the apex of theprotrusions of the film. The apertured formed film may be produced bythe vacuum forming and hydroforming processes mentioned above in amanner to create the apertures in the apex of the protrusions.

In still other embodiments, the protrusions may be created by deformingthe film using a pin plate as taught in U.S. Pat. No. 7,083,843, thedisclosure of which is incorporated herein by reference. In otherembodiments, the protrusions may be formed by deep embossing a precursorfilm, such as by passing a film through a nip formed between a firstroll having a plurality of spaced protrusions and a second anvil rollhaving a smooth, hard surface. As the film is passed through the nip,the film is deformed in the areas corresponding to the protrusions fromthe first roll. Deep embossing is disclosed, for example, in U.S. Pat.No. 5,229,186, the disclosure of which is incorporated herein byreference.

For three-dimensional films, the z-direction dimension of thethree-dimensional feature is a function of the diameter of the hole inthe forming screen. Other factors also contribute to the z-directionheight of the three-dimensional features such as film composition, basisweight of the film, and temperature of the film while being apertured.Typically, smaller diameter protrusions are shorter in z-direction thanlarger diameter apertures.

Three-dimensional formed films may comprise at least one thermoplasticpolymer. For example, three-dimensional formed films may comprise atleast one polymer selected from polyethylene, copolymers ofpolyethylene, low density polyethylene, linear low density polyethylene,high density polyethylene, medium density polyethylene, polypropylene,copolymers of polypropylene, blends of polyethylene and polypropylene,random copolymer polypropylene, polypropylene impact copolymers,polybutene, metallocene polyolefins, metallocene linear low densitypolyethylene, polyesters, copolymers of polyesters, plastomers,polyvinylacetates, poly (ethylene-co-vinyl acetate), poly(ethylene-co-acrylic acid), poly (ethylene-co-methyl acrylate), poly(ethylene-co-ethyl acrylate), cyclic olefin polymers, polybutadiene,polyamides, copolymers of polyamides, polystyrenes, polyurethanes, poly(ethylene-co-n-butyl acrylate), polylactic acid, nylons, polymers fromnatural renewable sources, biodegradable polymers or blends thereof.

Typically, the olefin monomer is either ethylene or propylene, butthermoplastic polyolefins may include higher molecular weight olefins.For example, polyolefins may also include polymers and copolymers ofolefin monomers such as, but not limited to, ethylene, propylene,butene, isobutenes, pentene, methyl pentene, hexene, heptene, octene,and decene. Functionalized olefin monomers, such as linear low densitypolyethylene-g-maleic anhydride (LLDPE-g-MA) available from E.I. du Pontde Nemours & Co., Inc., Wilmington, Del., under the trade designationBYNEL, may also be used.

The layers of the masking films can also contain elastic or semi-elasticpolymers. Examples of such elastic, or semi-elastic polymers include lowcrystallinity polyethylene, metallocene catalyzed low crystallinitypolyethylene, ethylene vinyl acetate copolymers (EVA), polyurethane,polyisoprene, butadiene-styrene copolymers, styrene block copolymerssuch as styrene/isoprene/styrene (SIS), styrene/butadiene/styrene (SBS),or styrene/ethylene-butadiene/styrene (SEBS) block copolymers, andblends of such polymers. Additionally, the elastic material may compriseother modifying elastic or non-elastomeric materials. Examples ofelastomeric block copolymer are sold under the brand name KRATON, byKraton Polymers, LLC.

Additionally, any of a variety of fillers may be added to thethermoplastic polymers and may provide certain desired characteristics,including, but not limited to, roughness, anti-static, abrasionresistance, printability, writeability, opacity and color. Such fillersare well known in the industry and include, for example, calciumcarbonate (abrasion resistance), mica (printability), titanium dioxide(color and opacity) and silicon dioxide (roughness). Typically, theolefin monomer is either ethylene or propylene, but thermoplasticpolyolefins may include higher molecular weight olefins. For example,polyolefins may also include polymers and copolymers of olefin monomerssuch as, but not limited to, ethylene, propylene, butene, isobutene,pentene, methyl pentene, hexene, heptene, octene, and decene.

The adhesion layer is capable of adhering to the surface of a substrateand the release layer provides a three-dimensional release surface whichreduces the tendency of the film to adhere to itself when stored on aroll. In addition, the release surface can provide cushioning andprotection to the surface of the substrate, without scratching thesurface and may also allow protected surfaces to be handled more easily.The release layer can be formulated to provide a significant portion ofthe strength and protective properties to the masking film, if desired.The resins, additives and process variables of the contacting filmsurfaces are designed to eliminate any residue or stain transfer to theoptical surfaces.

As will be appreciated from the above discussion, the loft of theprotrusions may be varied by modifying the amount of vacuum pressure,fluid pressure, temperature, dwell time, aperture size in the formingstructure and polymers used to make the film.

The thickness of an unembossed film is normally between 12.7μ and152.4μ, but more typically within a range of 12.7μ and 76.2μ. After adeep embossing process, such a film will have three-dimensional featuresbetween 63.5μ and 1069μ. The deep embossed film for use as a componentof a masking film may have between about 4 and about 120 macro cells perinch. In embodiments of the masking film, cells of the film have anyshape and may be arranged in many patterns. The shapes of the cellsinclude, but are not limited to, circles, ovals, diamond, boat shaped,ridges, channels, triangles, quadrilaterals or increasing multi-sidedfigures.

An embossed film may be made by any suitable process which addsthree-dimensional features to the film. For example, a web ofthermoplastic film may be fed through the nip of a driven pull roll orthe web may be fed through the nip of embossing rolls, for example, toform the embossing or deep embossing. Other processes may be used toemboss the films with the desired properties and dimensions. Prior tothe embossing process, the film may be preheated to facilitate embossingthe film and set the features into the film after cooling. For example,spaced apart heaters on either side of the film may be used to raise thetemperature of the film above its softening point. The heat softenedfilm may then be passed into a nip formed by a metal embossing roll anda backup roll covered with an outer layer of a resilient material, suchas a rubber, rubber-like material, or rubber silicone. In someembodiments, the backup roller may have a surface roughness to provide amatte surface on the film. For example, the backup roll may have asurface roughness of 5 to 150 microinch (0.127 to 3.81μ). In someapplications, a rubber roll may be used and have a surface roughnessbetween 30 and 100 microinch (0.762 and 2.54μ). In such an embodiment,the film is produced with a matte surface on one side and an embossedsurface on the other.

In certain other embodiments, the film may then be passed into a nipformed by a polished metal roll, such as a high polish smooth chromeroll, and a rough backup roll. This process will produce film with amatte surface and a smooth opposite surface, such a film has one releasesurface and may be laminated with an adhesion layer or may be laminatedto other layers that provide a second release surface, for example.

An adhesion layer is a layer of material that has some adhesiveproperties to smooth or rough surfaces and may be formed into a coherentmonolayer. In use, the adhesion layer is applied to the surface to beprotected. In certain embodiments, the masking films of the presentdisclosure achieve the desirable wetting and adhesion characteristicswithout an adhesive coating. In preferred embodiments of the maskingfilm, the adhesion layer comprises a smooth surface having a roughnessof from 0 to 60 microinch (0 to 1.524μ), or more preferably, between 0and 30 microinch (0 and 0.762μ).

The adhesion layer may comprise a polymer. The polymer of the adhesivelayer may be at least one polymer selected from polyethylene, lowdensity polyethylene, linear low density polyethylene, high densitypolyethylene, medium density polyethylene, polypropylene, randomcopolymer polypropylene, polypropylene impact copolymers, metallocenepolyolefin, metallocene linear low density polyethylene, plastomers,poly (ethylene-co-vinyl acetate), copolymers of an acrylic acid, poly(ethylene-co-acrylic acid), poly (ethylene-co-methyl acrylate), cyclicolefin polymers, polyamides, or poly (ethylene-co-n-butyl acrylate).

Embodiments of the masking film of the present disclosure comprise anadhesion layer comprising a metallocene polyolefin. As used herein, a“metallocene polyolefin” is a polyolefin produced by a metallocenecatalyzed polymerization of olefin monomers. Typically the olefinmonomer is either ethylene or propylene, but metallocene polymerizationsmay include a catalyst that may polymerize higher molecular weightolefins. Metallocene polyolefins also include copolymers of olefinsproduced by a metallocene catalyzed polymerization process, such ascopolymers of any combination of olefin monomers such as, but notlimited to, ethylene, propylene, butene, isobutenes, pentene, methylpentene, hexene, heptene, octene, and decene, for example, metallocenepoly (ethylene-co-octene) copolymers. Blends of metallocene polyolefinsmay also be used, as well as blends of metallocene polyolefins withother polymers. Metallocene polyolefins differ from polyolefins preparedby different polymerization processes. Metallocene polyolefins may becharacterized by narrow molecular weight distributions of less than 2.0,controlled polymer structure, higher thermal stability, higher clarity,and higher impact resistance. Based upon such properties, one skilled inthe art may easily discern between metallocene polyolefins andpolyolefins produced by other processes. Metallocene polyolefins arecommercially available, for example, from Dow Chemical Corp. and otherresin suppliers.

Any metallocene polyolefin having the desired properties may be used inembodiments of the masking film. For example, metallocene polyolefinselected from the group of polymers comprising metallocenepolyethylenes, metallocene polypropylenes, and metallocene copolymerscomprising monomer units derived from ethylene and propylene may be usedin the adhesion layer of the masking film. Such polymers provide adesired level of adhesive and cohesive properties. Metallocenecopolymers may also provide the desired properties to the adhesion layerof the masking films. Particularly, metallocene copolymers comprisingmonomer units derived from ethylene higher a-olefins having 3 to 12carbon atoms, for example, a metallocene poly (ethylene-co-octene).Though other metallocene copolymers may also be used, such asmetallocene copolymers comprising monomer units derived from ethylene,propylene, butene, pentene, hexene, and octene. In certain embodiments,it may be advantageous for the adhesion layer of the masking film tocomprise a metallocene copolymer comprising monomer units derivedprimarily of polyethylene and additional monomer units derived frombutene, pentene, hexene, octene, or a combination of these monomers.Blends of metallocene polyolefins may also be used.

Embodiments of the masking films include metallocene polyolefins havinga molecular weight distribution (i.e., polydispersity) greater than 1.0and less than 2.0, or in certain embodiments, metallocene polyolefinshaving a molecular weight distribution of less than 1.7 may be desiredor even a molecular weight distribution greater than 1.0 and less than1.5.

In addition, the adhesion layer may comprise polymers comprisingmetallocene polyolefins as blocks of the polymer, wherein the otherblocks may or may not comprise a metallocene polyolefin. Such blockcopolymers are considered metallocene polyolefins as the term is usedherein.

An embodiment of a two layer masking film comprises an adhesion layerand a release layer. The adhesion layer comprises a blend of metallocenepolyethylene and a low density polyethylene. The release layer compriseslow density polyethylene and has a release surface comprising aplurality of protrusions.

In such embodiments, the adhesion layer may be from 5% to 30%, or inother embodiments from 15% to 25%, of the film based upon the totalthickness of the masking film and the release layer may be the remaining70% to 90%, or in other embodiments from 75% to 85%, of the totalthickness of the masking film. In a more specific embodiment, theadhesion layer is 15% to 20% of the film. The masking film may compriseany polymers that give the desired properties. However, in oneembodiment, the adhesion layer consists essentially of 75% to 85% of ametallocene poly (ethylene-co-octene) copolymer and 15% to 25% of a lowdensity polyethylene. This embodiment has specific properties that allowrapid and sufficient wetting of low surface energy substrates such as,but not limited to substrates comprising glass, acrylates, cyclic olefinpolymers (“COP”) films, or triacetyl cellulose (“TAC”) films.

The masking films have particular use in the manufacture of opticalfilms for LCD displays such as optical grade light management film(polarizers) used in an LCD assembly. In certain applications, themetallocene poly (ethylene-co-octene) copolymer may be replaced with ametallocene plastomer or other metallocene polyolefin. TAC films aretypically used as polarizer protective layers in the manufacture ofLCD's. TAC polymers formed with the low stresses of solvent castingresult in a unique polymer system that meets the requirements ofextremely isotropic LCD coversheets. Such properties have allowedsolvent cast TAC films to capture the vast majority of LCD coversheetapplications. However, the TAC is a soft film and when produced androlled, the smooth front and back film surfaces have a tendency to stickor block together and generate poor wound roll quality. This may lead todefects in the LCD assembly. The masking film of the present disclosureprotects and allows easier handling of TAC films better than othercombinations of constituents and structures of masking films. Thus, TACfilms, when masked with films of this disclosure may be used moresuccessfully and efficiently for LCD assemblies.

Embodiments of the masking film with different adhesion levels may beproduced by incorporating the constituents in different percentages ofcertain polymers and co-polymers in the adhesion surface of the maskingfilm.

Secondary polymers such as polyolefins (homopolymers or co-polymers),polyvinyl alcohol, polyvinyl chloride, nylon, polyesters, styrenes,polybutylenes, polymethylpentene, plastomers, poly (ethylene-co-vinylacetate), poly (ethylene-co-acrylic acid), poly (ethylene-co-methylacrylate), cyclic olefin polymers, polyamides, or poly(ethylene-co-n-butyl acrylate) and polyoximethylene, and mixturesthereof, can be blended with the primary polymer at varying ratios toprovide the desired level of adhesion of the film. Acid-modifiedco-polymers, anhydride-modified co-polymers and acid/acrylate-modifiedco-polymers also are useful. Films of polyethylene are particularlysuited and therefore preferred. Films of low-density polyethylenehomopolymers are even more particularly suited, and therefore morepreferred, due to their relatively low tensile modulus which tends toconform better to surfaces.

The masking film may be any desired thickness. However, in certainapplications, the total thickness of the masking film is from 60μ to200μ.

An embodiment of a masking film is shown in FIG. 1. In FIG. 1, themasking film 10 is shown on substrate 16. Masking film 10 comprises anadhesion layer 12 and a release layer 14. The adhesion layer 12 isformulated to provide adhesion to the substrate 16, but also to beremoved when no longer needed without damaging the substrate 16 orleaving any residue on the substrate 16. Adhesion layer 12 can be of anydesired formulation now know in the art or later developed for theparticular surface being protected. As is also known in the art, theadhesion layer is preferably made with a very smooth surface tofacilitate intimate contact with the substrate surface.

As seen in FIG. 1, the release layer 14 comprises a three-dimensionalrelease surface 15. In this embodiment, the release surface 15 comprisesa plurality of protrusions 13 that are raised from the planar portion ofrelease surface 15. The raised protrusions create a physical separationbetween the masking film 10 and an adjacent substrate in a stack. Theplurality of protrusions 13 protect the substrate 16 during handling andallow one substrate to be separated from another more easily. In thisparticular embodiment, the release layer comprises a formed film inwhich protrusions 13 are integral extensions of the release layer 14.

The release surface 15 may comprise protrusions 13 that have an averageheight, as measured from the base surface 15 of the film, of greaterthan 50 microns. In certain embodiments, the average height of theprotrusions may be greater than 100 microns. In certain embodiments, therelease surface of the release layer comprises at least one of aplurality of protrusions, a plurality of three-dimensional apertures, adeeply embossed structure, or combinations thereof.

In the embodiment of FIG. 1, the three-dimensional protrusions 13comprise apertured protrusions in the shape of cones or funnels and havean opening or aperture 11 in the apex of the protrusion 13. It isunderstood, however, that the protrusions need not be apertured and, infact, are preferably not apertured. The apertures create an opportunityfor debris to collect or be trapped in the film. The debris can thenscratch or otherwise damage the substrate surface. It will beappreciated and understood that the three dimensional film used asrelease layer 14 can be oriented in the direction opposite the directionshown in FIG. 1, wherein the protrusions 13 would be oriented towardsand in contact with adhesion layer 14.

FIG. 1A shows another embodiment of a masking film 110 is adhered to asubstrate 116. The masking film 110 comprises an adhesion layer 112 anda release layer 114. The release layer 114 has a release surface 115comprising a plurality of three-dimensional protrusions 113 extendingfrom the release surface 115. In the embodiment of FIG. 1A, the releaselayer 114 may conveniently be formed by a deep embossing process.

With reference to FIG. 1B, another embodiment of the masking film isshown. In this embodiment, the masking film 210 is shown adhered to asubstrate 216. The masking film 210 comprises an adhesion layer 212 anda release layer 214. The release layer 214 in this embodiment comprisesa multiplanar film. On one side, the multiplanar film 214 has aprotrusions 213 extending upward from a planar surface 215 of the film.On the opposite side, the multiplanar film has a plurality ofprotrusions 217 that, in the embodiment shown, terminate in apertures218 at the apex of the protrusion. As noted above, it will beappreciated that the film used as the release layer 214 may be invertedsuch that the protrusions 213 are oriented toward and in contact withthe adhesion layer 212.

Embodiments also include masking films comprising more than two layers.A specific embodiment of a masking film comprises an adhesion layer, acore layer, and a release layer. At least one core layer may beinterposed between the adhesion layer and the release layer of themasking film. The core layer(s) of such embodiment may comprise anypolymer that improves the mechanical properties of the film, such asstiffness, modulus, tear resistance, etc. For example, the core layermay be formulated to reduce the potential damage of the smooth surfaceof the adhesion layer during manufacturing and use of the film, or toimprove the film's modulus. In certain embodiments, the masking filmshould have a modulus of greater than 15,000 psi (103.4 MPa). In certainembodiments, the modulus of the masking film may be greater than 15,000psi (103.4 MPa) and less than 350,000 psi (2413.17 MPa). In certainembodiments, the release layer should have a modulus of 240,000 psi(1654.74 MPA) (±15%). The modulus in this range is desired to provideprotection to the adhesion layer without affecting the wettingcharacteristics of the masking film.

For example, the core layer may be any thermoplastic, thermoset, orelastic polymer, as described herein, for example, that provides thedesired properties to the masking film. In certain embodiments, the corelayer may comprise a polymer selected from polyethylene, low densitypolyethylene, linear low density polyethylene, high densitypolyethylene, medium density polyethylene, polypropylene, randomcopolymer polypropylene, polypropylene impact copolymers, metallocenepolyolefin, metallocene linear low density polyethylene, plastomers,poly (ethylene-co-vinyl acetate), copolymers of an acrylic acid, poly(ethylene-co-acrylic acid), poly (ethylene-co-methyl acrylate), cyclicolefin polymers, polyamides, poly (ethylene-co-n-butyl acrylate),polyvinyl chloride, nylon, polyester, and combinations thereof. The corelayer can aid in providing the desired opacity and/or color, stiffnessand toughness to the multilayer masking film.

Embodiments of the masking film may comprise two release surfaces. Thefilms with two release surfaces may be monolayer or multilayer films.

FIG. 2 depicts an embodiment of a masking film 20 comprising a corelayer 21, a first release layer 22 and a second release layer 26. Eachrelease layer 22, 26 has a release surface 23, 27, respectively. Therelease surfaces 23, 27 comprise three-dimensional surfaces having aplurality of protrusions 24, 28, respectively. The protrusions areintegral extensions of the release layers. In the embodiment shown inFIG. 2, the three-dimensional protrusions 24, 28 are unapertured, butstill have a characteristic cone shape of a vacuum formed, orhydroformed, film.

Other embodiments of the masking film may omit the core layer 21 andmay, for example, comprise two three-dimensional films laminatedtogether such that the three-dimensional surfaces are orientedoutwardly.

The release surfaces on both sides of the masking film may be similar ordiffer in structure or properties. For example, the release surfaces mayhave different structures, patterns, loft, mesh count, or can be madefrom different materials. FIG. 3 depicts an embodiment of a single layermasking film 30 comprising two release surfaces 31, 32. Release surface31 comprises a three-dimensional surface having a plurality ofembossments 33. Release surface 32 comprises a matte surface having asurface roughness of between 5 and 100 microinch (0.127μ and 2.54μ).

With reference now made to FIG. 4, a masking film 40 comprises a releaselayer 42 and an adhesion layer 44. The release layer 42 comprises arelease layer 46 having a plurality of spaced apart raised ribs orridges 48. Such films may be conveniently made by casting a moltenpolymer onto a forming drum having raised ribs or wires. As the polymercools to form the film, the film surface will correspond to the ribs orwires, resulting in continuous raised ridges 48 in the film. The releaselayer 42 can then be coated or laminated to an adhesion layer 44.Alternatively, the masking film 40 can be made by coextruding therelease layer 42 and the adhesion layer 44 onto a forming structurehaving a plurality of spaced apart channels or grooves and thensubjecting the coextrusion to a vacuum (as discussed above) to draw thepolymer forming the release layer into the grooves. As the polymercools, the film will form ridges corresponding to the location where thepolymer was drawn into the groove. Care must be taken to ensure that thesurface of the release layer 44 does not get drawn into the grooves sothat the adhesion layer remains as smooth as possible. Other methods ofmaking the films may also be used to advantage.

FIG. 4A depicts a cross sectional view of the release layer 42 of theembodiment of FIG. 4. In the embodiment shown in FIG. 4A, the maskingfilm is a monolayer film 42 having a release surface 46 comprising aplurality of spaced apart, three-dimensional raised ridges 48 formedintegral with the release surface 46 as in FIG. 4. The masking filmfurther comprises a second surface 43 opposite the release surface 46.Second surface 43 of release layer 42 has a plurality of air spaces 54corresponding to the underside of the raised ribs 48.

The ridges 48 in the embodiments of FIGS. 4 and 4A provide a significantrigidity to the films. This is advantageous for the embodiment of FIG.4A in particular where the film may be used as a replacement for paperin a stack of substrates.

FIGS. 5 and 5A shows a masking film 50 comprising a release layer 52 andan adhesion layer 54. Release layer 52 comprises a release surface 56having a plurality of polymeric beads 58 disposed thereon. In contrastto the other embodiments described above, the beads 58 are not formed asintegral extensions of the release layer 52. Rather, the beads 58comprise individual, discrete beads of polymeric material, such aspolyethylene, applied to the surface of the film.

Polymer beads can be applied via an impact printing process (such agravure printing), a non-impact printing process (such as ink jetprinting), a glue application apparatus, or any other apparatus capableof ejecting or depositing discrete polymer beads in molten, semi-molten,or solid form.

In other embodiments, discrete polymer beads may be applied to thesurface of the release layer while the beads are in a solid form and therelease layer is in a semi-molten or softened state. In otherembodiments, the beads will be applied while the polymeric material isat, above or near the melting temperature. To keep the beads fromspreading into the film layer, it may be advantageous to quench thepolymer bead by contacting the surface of the release layer with aquenching roll.

The polymer beads 58 may comprise any polymer material that can beapplied to the release layer 56 and remain sufficiently adhered to therelease layer for the intended purpose. The polymer beads may be of anysize, shape, dimension, pattern or spacing desired for the particularuse of the film.

FIG. 6 depicts an embodiment of a masking film 60 having a planarportion 61 and a plurality of protrusions 62 formed integral with theplanar portion 61. The protrusions 62 extend on either side of theplanar portion 61. In the embodiment shown, the protrusions 62 are inregistration on either side of the film, but this does not necessarilyneed to be the case.

FIG. 7 is a schematic illustration of one process that may be used toproduce the masking films. The polymers are mixed and melted in anextruder (not shown) and passed through a die 70, where the polymeremerges in a molten stream or curtain 72 onto roll 74. Depending on theembodiment being produced, roll 74 may comprise a smooth casting roll, aforming structure, or a textured casting roll. Web 76 is broughttogether with web 72 at the nip formed between roll 74 and roll 78. Thetwo webs, 72, 76 are laminated in the nip and then removed from roll 74to produce the final film structure 80. If desired, a vacuum may beapplied to assist in the lamination, as is known in the art and taught,for example, in U.S. Pat. No. 4,995,930, incorporated herein byreference. Again, depending on the particular embodiment being produced,the web 76 may be an apertured or unapertured three-dimensional film, anembossed film, a deep embossed film, an adhesive layer, etc.

For example, if desired to make the masking film 10 of FIG. 1, thepolymeric material intended for use as the adhesion layer 12 would beextruded from die 70 as molten web 72 onto roll 74, which in this casewould comprise a smooth surface chill roll. Web 74, comprisingthree-dimensional apertured film 14 of FIG. 1, would be brought intocontact with the web 72 at the nip formed between pressure roll 78 andchill roll 74. The combination of heat and pressure at the nip wouldcause the apertured film 76 to become adhered to the adhesion layer 72whereby the laminated film 10 of FIG. 1 would emerge as web 80.

If the masking film 20 from FIG. 2 was desired, the web 72 couldcomprise a coextrusion of the materials for first release layer 22 andcore layer 21 which would be cast onto roll 74, which in such anembodiment would comprise a forming structure. The second release layer26 would be brought into the nip as web 76. By applying vacuum to theweb 72 through the forming structure 74, as is known in the art, thesecond release layer 26 would be formed and the final film 20 wouldemerge from roll 74 as web 80.

FIG. 8 illustrates a schematic diagram of another process that may beused to produce certain of the embodiments. In the process of FIG. 8, amolten polymer web 82 is extruded from die 80 onto roll 84. As with theprocess of FIG. 7, roll 84 may comprise a forming structure, a smoothsurface casting roll, a textured surface casting roll, an embossingroll, etc. Nip roll 86 can preferably comprise a textured roll orembossing roll, but may also be a smooth roll if desired. The process ofFIG. 8 is particularly advantageous in making masking films such as theembodiments shown in FIGS. 3, 4A and 6, for example. In the embodimentof FIG. 6 in particular, the nip roll 86 may be a thin screen disposedon a support roll of rubber or other material, The thin screen wouldimpart the surface topography to one side of the film while the surfaceof roll 84 would impart the surface topography to the opposite side ofthe film, preferably with the assistance of vacuum.

The masking films may be interleaved between stacks of substrates toprotect the substrates during shipping, use, manufacture, or assembly.The masking films may be particularly useful for use in stacks ofsubstrates with smooth surfaces, such as glass or other optical media.The masking film may be placed in between substrates to protect thesubstrates and allow the desired release characteristics.

A masking film that resists buildup of an electrostatic charge isdesirable in many applications. In certain applications, the maskingfilm protects portions of the film not only from mechanical damage andchemical damage or contamination, but also from contamination fromparticulates, such as dust. Therefore, it is desired in certainapplications, such as layered optical screens, that the masking filmsthemselves do not transfer dust or other particles to the surface of thesubstrate. In order to improve the antistatic properties of the maskingfilm, an antistatic agent may be added to the adhesion layer and/or therelease layer. Preferably, the adhesion layer or release layer willinclude an antistatic agent that will not migrate to the surface of thefilm and, thus having the potential of contaminating the surface of thesubstrate, such as an ionomer. Therefore, to reduce the dust on thesurface, the adhesion layer in specific embodiments may comprise anionomer. An ionomer is a polymer having unique physical properties dueto ionic interactions of discrete regions of the polymer components.Most ionomers are polymers in which a small but significant proportionof the constituent monomers have ionic groups. In certain embodiments,the ionomer may be a potassium ionomer.

Without affecting the basic and novel characteristics, any layer of themasking films of the present disclosure may comprise at least oneanti-oxidant, colorant, pigment, clarifier, and/or nucleating agent.

In a preferred embodiment, when a multiple layered film is used in thedisclosure, any layer, such as the adhesion layer, a core layer and/orrelease layer, may be co-extruded using any co-extrusion process knownin the art. The use of co-extrusion allows for the relatively simple andeasy manufacture of a multi-layered masking film composed of distinctlayers, each performing specific functions. Although co-extrusion of theimproved multi-layered masking film of the present disclosure ispreferred, it is again noted that the masking film can be mono-layeredor multi-layered and that, regardless of form, the masking film can beproduced using any other suitable method, if desired.

Any of a variety of conventional methods can be utilized for applyingthe multi-layer (or monolayer) masking film to the textured surface ofthe substrate to be protected. Preferably, the multi-layer film is takenoff from a roll and directly applied to the surface by means of a niproll or similar system. In this manner, the smooth side of themulti-layer film is applied to and pressed against the texturedsubstrate in one operation. If desired, the resulting lamination may bepassed through compression rolls or the like for further processing.Other suitable techniques for forming the laminations of this disclosurewill be readily apparent to those skilled in the art upon reading thedescription herein.

EXAMPLES

Many other variations, modifications, and alternate embodiments may bemade in the article and techniques described, by those skilled in theart, without departing from the concept of the present disclosure.Accordingly, it should be clearly understood that the article andmethods referred to in the foregoing description and following examplesare illustrative only and are not intended as limitations on the scopeof this disclosure.

Example 1

A series of films were prepared having the compositions of Table 1.

TABLE 1 No. Adhesion Layer Release Layer 1 97.5% Low densitypolyethylene 100% low density polyethylene vacuum 2.5% of slip agentmasterbatch (1% dimpled in an 11.2 mesh hex pattern slip agent in lowdensity polyethylene) 2 97.5% Low density polyethylene 100% low densitypolyethylene film 2.5% of slip agent masterbatch (1% vacuum dimpled in a22 mesh hex slip agent in low density polyethylene) pattern 3 97.5% Lowdensity polyethylene 24 GSM cast film of low density, linear 2.5% ofslip agent masterbatch (1% low density, high density polyethylene slipagent in low density and white pigment concentrate polyethylene)embossed in a Rombo pattern 4 97.5% Low density polyethylene N/A 2.5% ofslip agent masterbatch (1% slip agent in low density polyethylene) 597.5% Low density polyethylene 24 GSM cast film of low density, linear2.5% of slip agent masterbatch (1% low density, high densitypolyethylene slip agent in low density and white pigment concentratepolyethylene) embossed in a Rombo pattern 6 97.5% Low densitypolyethylene Vacuum formed apertured film of high 2.5% of slip agentmasterbatch (1% and low density polyethylene with an slip agent in lowdensity polyethylene) 8.75 mesh hex pattern 7 12%styrene-ethylene/butylene- 97.5% Low density polyethylene styrene blockcopolymer 2.5% of slip agent masterbatch (1% slip 88% R2002 Bynel ®resin agent in low density polyethylene) 8 12%styrene-ethylene/butylene- 100% low density polyethylene vacuum styreneblock copolymer dimpled in an 11.2 mesh hex pattern 88% R2002 Bynel ®resin 9 12% styrene-ethylene/butylene- Vacuum formed apertured film ofhigh styrene block copolymer and low density polyethylene with an 88%R2002 Bynel ® resin 8.75 mesh hex pattern 10 12%styrene-ethylene/butylene- 100% low density polyethylene film styreneblock copolymer vacuum dimpled in a 22 mesh hex 88% R2002 Bynel ® resinpattern 11 12% styrene-ethylene/butylene- 24 GSM cast film of lowdensity, linear styrene block copolymer low density, high densitypolyethylene 88% R2002 Bynel ® resin and white pigment concentrateembossed in a Rombo pattern

Sample No. 4 is a monolayer film. Sample no. 7 is a coextruded film. Allother samples were prepared by laminating two films together. The samplefilms were measured for basis weight, haze and thickness (loft) andtested for adhesion. Properties and data are set forth in Table 2.

TABLE 2 Basis Weight Thickness Sample No. (gsm) Haze (%) (mm) Adhesion(g) 1 48.13 27.6 0.131 25.3 2 47.79 59.6 0.114 49.0 3 48.05 — 0.079 22.34 25.20 85.3 0.031 114.8 5 48.74 — 0.080 48.0 6 54.99 46.6 0.358 5.6 726.00 84.0 0.034 792.0 8 53.18 26.4 0.173 333.9 9 56.02 45.5 0.560 53.110 47.86 51.3 0.089 431.7 11 52.13 — 0.083 439.9

Example 2

A series of monolayer polyethylene films were made having one smoothadhesion surface and an opposite release surface. The films were made bycasting the low density polyethylene/slip agent blend used in theearlier examples onto a smooth chill roll. Pressure was applied to theopposite side of the film with a textured or engraved embossing roll, asseen in FIG. 8. The textured embossing roll was made of rubber and had asurface texture with a roughness of 1.397μ (55 microinch). The engravedembossing roll was also made of rubber and had an series of deepengraved grooves in a diamond shape pattern. Each surface of the filmwas then tested for adhesion using a special developmental adhesionstrength test method in a 180° peel test. Results are reported in Table3.

TABLE 3 Textured Engraved embossed Release Surface release surface BasisEmbossed Embossed Sample Weight Thickness Thickness No. (gsm) (mm)Adhesion (g) (mm) Adhesion (g) 12 70 .100 194 .100 185 13 80 .110 206.103 160 14 90 .124 267 .155 230

Example 3

A series of polyethylene films were made having a release surface oneach side. The films were made by casting the low densitypolyethylene/slip agent blend used in the earlier examples onto anengraved chill roll. The chill roll had an engraved surface containing aseries of deep engraved grooves in the shape of a diamond pattern.Pressure was applied to the opposite side of the film with a texturedembossing roll, as seen in FIG. 8. The textured embossing roll was madeof rubber and had a surface texture with a roughness of 1.397μ (55microinch). Each surface of the film was then tested for adhesion.Results are reported in Table 4. As seen in Table 4, in this embodiment,the films did not adhere to the substrate.

TABLE 4 Embossed Thickness (mm) Adhesion (g) Sample Basis weightTextured Engraved Textured Engraved No. (gsm) side side side side 15 370.060 0.060 0 0 16 46 0.060 0.080 0 0 17 55 0.076 0.092 0 0

Example 4

A series of three-layer coextruded films were prepared having thecomposition set forth in Table 5 (layer 2 was the core layer and layers1 and 3 are outer or “skin” layers). The films were cast onto a formingscreen having thin wires wrapped about the periphery and subjected tovacuum to form the film materials depicted in FIG. 4A. The films weretested for a variety of physical properties. Results are reported inTable 6.

TABLE 5 Sample No. Layer 1 Layer 2 Layer 3 17 HDPE 88% MDPE HDPE 12%LDPE 18 HDPE 88% MDPE HDPE 12% LDPE 19 HDPE 60% CaCO₃ HDPE 30% MDPE 10%LDPE 20 HDPE 86% MDPE HDPE 12% LDPE  2% TiO₂ 21 HDPE 86% MDPE HDPE 12%LDPE  2% TiO₂ 22 HDPE 86% MDPE HDPE 12% LDPE  2% TiO₂

TABLE 6 Sample No. 17 18 19 20 21 22 Basis Weight (gsm) 49.1 69.5 38.839.3 61.4 31.2 Gurley Surface GU 157 168 123 169 167 139 Embossedthickness (mm) 0.475 0.453 0.202 0.369 0.533 0.307 Circular bendstiffness (gmf) 443 1084 167 352 806 238 Compressibility (%) 30.8 18.432.4 36 22.5 4.15 Resiliency (%) 85.4 93.3 86.4 78.7 89.5 81.22 SecantModulus @1% strain (Kgf) 30.5 46.3 23.5 24.8 37.3 19.4 Modulus (psi)165,887 209,892 209,071 130,811 199,071 102,677 Peak Load (gf/inch) 34634364 1604 2884 4561 2618 Elongation @ break (%) 630 538 11 652 690 654

1. A film comprising an adhesion layer and a release layer, said releaselayer comprising a release surface having a plurality ofthree-dimensional protrusions.
 2. The film of claim 1, wherein thethree-dimensional protrusions are integral extensions of the releaselayer.
 3. The film of claim 2, wherein the protrusions are vacuum formedprotrusions.
 4. The film of claim 2, wherein the protrusions arehydroformed protrusions.
 5. The film of claim 2, wherein the protrusionsare mechanically deformed protrusions.
 6. The film of claim 5, whereinthe protrusions are deep embossed protrusions.
 7. The film of claim 2,wherein the protrusions comprise ridges extending substantially thelength of the film.
 8. The film of claim 1, further comprising at leastone intermediate layer disposed between the release layer and theadhesion layer.
 9. The film of claim 1, wherein the three-dimensionalprotrusions comprise discrete polymeric beads.
 10. A film comprising afirst release surface and a second release surface, at least one of saidfirst and second release surfaces having a plurality ofthree-dimensional protrusions.
 11. The film of claim 10, wherein thethree-dimensional protrusions are integral extensions of the releaselayer.
 12. The film of claim 11, wherein the protrusions are selectedfrom vacuum formed protrusions; hydroformed protrusions; andmechanically deformed protrusions.
 13. The film of claim 11, wherein theprotrusions comprise ridges extending substantially the length of thefilm.
 14. The film of claim 10, comprising a multilayer film.
 15. Thefilm of claim 10, wherein the three-dimensional protrusions comprisediscrete polymeric beads.
 16. The film of claim 10, wherein the firstrelease surface comprises three-dimensional protrusions and wherein saidsecond surface comprises a matte surface.
 17. The film of claim 10,wherein both the first and second release surfaces comprisethree-dimensional protrusions.
 18. A method of protecting a substratesurface comprising placing a film in intimate contact with saidsubstrate surface, said film comprising at least one release layerhaving a release surface, said release surface having a plurality ofthree-dimensional protrusions.
 19. The method of claim 18, wherein saidfilm is positioned between two adjacent substrate surfaces in a stack ofsubstrates.
 20. The method of claim 18, wherein the film is selectedfrom a) a film having an adhesion layer and a release layer; b) a filmhaving an adhesion layer, a release layer, and at least one core layerintermediate the release layer and the adhesion layer; c) a film havinga release layer and a matte surface opposite the release surface; and d)a film having a second release layer, said second release layer having aplurality of three-dimensional protrusions.